1. Field of the Invention
The present invention relates to a feeding apparatus for feeding a recording medium such as a sheet material, a film material or a cut paper sheet one by one, and a recording apparatus equipped with such feeding apparatus.
2. Related Background Art
As a recording apparatus for recording a character or an image on a recording medium such as a cut paper sheet, there have conventionally been known an ink jet recording apparatus, a thermal transfer recording apparatus, an electrophotographic recording apparatus, etc.
Among these, a smaller configuration of the entire recording apparatus and a lower production cost are requested for the ink jet recording apparatus and the thermal transfer recording apparatus as they are often used in personal applications.
FIG. 21 is an external perspective view of a prior ink jet recording apparatus. In FIG. 21, a recording medium 200 is set in an automatic sheet feeding apparatus (hereinafter represented as ASF) 201. The ASF 201 is provided with a cover 202 for a main body of a recording portion having an ink jet recording portion therein. The ASF 201 is provided with a discharge tray 203 for supporting a recording medium after recording.
FIG. 22 is a perspective view of the ASF only in FIG. 21, in the course of a feeding operation.
Referring to FIG. 22, The ASF 201 is provided with an ASF base 209 for setting the recording medium 200. The ASF base 209 supports a feeding roller shaft 203, on which provided is a feeding rubber 206. FIG. 23 is a cross-sectional view showing the feeding rubber 206. As shown in FIG. 23, the feeding rubber 206 has a D-shaped cross section, and it is moved, prior to a feeding operation, to a position where a straight portion of the D-shape is opposed to the recording medium thereby preventing a friction between the recording medium and the feeding rubber 206. The recording medium is set along a pressure plate 210, which is brought closer to the feeding rubber 206 only in a feeding operation and is contacted with the recording medium 200 by a power of an unillustrated compression spring provided behind the pressure plate 210. The feeding roller shaft 203 receives a driving power from an unillustrated motor through a gear train 207, and is rotated in a direction to convey the recording medium 200 from the ASF base toward an unillustrated recording portion. A sensor masking portion 204, integrally formed on the feeding roller shaft 203, rotates together with the feeding roller shaft 203 and masks or exposes a transmission photosensor 205 fixed on an unillustrated substrate. The pressure plate 210 is contacted with and separated from the feeding roller 206, in synchronization with one turn of the feeding roller shaft 203.
A configuration executing such elevation and lowering of the pressure plate in synchronization with a rotating operation of the feeding roller shaft is disclosed for example in Japanese Registered Patent No. 3090161.
In an initial operation state of the ASF 201, the feeding roller shaft 203 is in such a rotational position that the sensor masking portion 204 masks the transmission photosensor 205. In such state the pressure plate 210 is separated from the feeding rubber 206. In case it is in a non-masking position, an initializing operation is executed by an initialization signal from the main body of the ink jet recording apparatus. In case it is in a masking position, after the entry of a recording signal, the feeding roller shaft 203 starts rotation and the pressure plate 210 approaches the feeding rubber 206, whereby the feeding rubber 206 comes into contact with the recording medium 200 thereby executing a feeding thereof. The recording medium 200 thus fed is separated into a sheet in a separating portion 208 and conveyed to the recording portion.
However, the prior recording apparatus described above has been associated with following drawbacks.
Firstly, in the prior recording apparatus, it is necessary to establish an initial position for the feeding operation, in order to prevent a frictional contact between the recording medium and the feeding roller rubber, and a position sensor is provided for this purpose. Therefore the prior recording apparatus requires a complex electrical structure with an increased production cost. Also since a drive control is executed for stopping a motor in response to a detection signal from the sensor, it is necessary to secure a precision in the stopping position of the motor. Therefore, a highly precise motor is required, leading to an increase in the production cost.
By forming the feeding roller rubber in a circular shape instead of the D-shape, it is no longer necessary to initialize the rotational position of the feeding roller rubber, but the position of the pressure plate needs to be initialized. In the prior configuration, a sensor is still required to initialize the pressure plate, thereby elevating the production cost as in the above-described configuration.
Secondly, in case the distance from the feeding roller rubber to the recording portion is made long, the feeding roller rubber is required to have a circumferential length at least equal to the feeding distance to the recording portion, so that it has to have a large diameter, thus increasing the dimension of the entire recording apparatus.
Particularly in an ASF of so-called cassette feeding type in which the recording media are set horizontally, instead of the above-described ASF which is provided in the conventional recording apparatus and in which the recording media are placed on a pressure plate in a state inclined from the horizontal direction, the diameter of the feeding roller directly influences the height of the entire recording apparatus. Therefore, such ASF is difficult to employ in realizing a recording apparatus of a reduced height, thus resulting in a large installation space.
Also, together with an increase in the size of the entire recording apparatus, an external casing, such as a cover, for the entire apparatus also becomes larger, thus resulting in an increase in the cost of the material for forming the external casing etc. and elevating the production cost.
Particularly in case of employing a feeding roller rubber of a D-shaped cross section for preventing frictional contact between the recording medium and the feeding roller rubber as in the prior recording apparatus described above, the circumferential length of the arched portion of the feeding roller rubber, other than the straight portion thereof, has to be made longer than the feeding distance to the recording portion. Therefore, an even larger diameter is required than in the feeding roller rubber of the circular shape, thus being difficult to use in realizing a recording apparatus of a reduced height.
Thirdly, the prior recording apparatus utilizes the biasing force of a compression coil spring provided at the rear side of the pressure plate, as pressurizing means for pressing the pressure plate to the feeding roller rubber. For this reason, a medium stacking portion for stacking the recording media becomes thicker by the length of such compression coil spring, thereby leading to an increase in the dimension of the entire apparatus. This drawback becomes more conspicuous, as in the case of the roller diameter mentioned above, in so-called cassette feeding in which the recording media are stacked horizontally.